<?php
/**
 * Created by PhpStorm.
 * User: zhang
 * Date: 2018/2/9
 * Time: 11:22
 */

$arr = [
	"C"      => "I am the GOD",
	"php"    => "PHP is the best language int the world",
	"Python" => "Life is short, I use Python",
	"Java"   => "Write once, run anywhere",
	"Go"     => "better C",
];

$arrUpper = array_change_key_case( $arr, CASE_UPPER );
/**
 * Array
 * (
 * [C] => I am the GOD
 * [PHP] => PHP is the best language int the world
 * [PYTHON] => Life is short, I use Python
 * [JAVA] => Write once, run anywhere
 * [GO] => better C
 * )
 */
print_r( $arrUpper );

$arrLower = array_change_key_case( $arr, CASE_LOWER );
/**
 * Array
 * (
 * [c] => I am the GOD
 * [php] => PHP is the best language int the world
 * [python] => Life is short, I use Python
 * [java] => Write once, run anywhere
 * [go] => better C
 * )
 */
print_r( $arrLower );
